Glycerol, an endogenous molecule, is a trihydroxy alcohol that has a key role in the skin. Endogenous glycerol notably plays a major role in hydration of the skin, in skin elasticity and in repair of the epidermal barrier (British Journal of Dermatology, 159(1):23-34, July 2008, Fluhr, J. W.; Darlenski, R. *; Surber).
The various beneficial effects of glycerol on the epidermis notably include hydration of the stratum corneum (the outermost layer of the skin), the barrier function of the skin, the mechanical properties of the skin, protection against irritant stimuli and acceleration of the process of wound healing (British Journal of Dermatology, 159(1):23-34, July 2008, Fluhr, J. W.; Darlenski, R. *; Surber).
It is also known from the prior art that topical application of products containing glycerol improves the properties of the skin in diseases characterized by xerosis and by an epidermal barrier that has deteriorated, as is the case in atopic dermatitis.
Moreover, with age, we observe a decrease in the amount of glycerol in the skin.
It can be deduced from all of the foregoing that supplementation of glycerol is beneficial for the skin.
That is why many cosmetics have glycerol in their composition. Thus, with application once or twice a day, the skin benefits from the positive effects of glycerol. However, this solution requires topical treatment of the skin every day.
Just like the use of a cosmetic, injection of an aqueous solution of glycerol in the skin makes it possible to benefit from the positive effects of glycerol in the very short term. In fact, almost all of the glycerol injected migrates rapidly from the zone of injection to the stratum corneum, and then is removed from the surface of the skin by daily washing. Thus, the beneficial action of glycerol is “one-off” (PNAS, 100(12):7360-7365, June 2003, Hara, M. W.; Verkman, A. S./Journal d'Investigation Dermatologique, 125: 288-293, 2005, Choi, H. C).
Injectable solutions of glycerol containing hyaluronic acid (HA) are described in the prior art. Owing to their viscoelastic characteristics, these solutions appear to allow delayed release of glycerol. However, when injected into the skin, these solutions do not provide long-term supplementation of glycerol (supplementation for a period of at most one week). In fact, hyaluronic acid is metabolized within the skin in less than a week (Wenner-Gren International series; The chemistry, biology and medical applications of hyaluronan and its derivatives, Laurent, T. C.).
Consequently, an injectable hydrogel providing gradual, long-term release of glycerol in the skin does not exist in the prior art.